FIELD OF INVENTION:
The present invention is directed to a very simple and low cost photosensor based
automatic online length measuring system for moving products avoiding operator's
involvement especially in hazardous/accident prone sites. The system is adapted to
directly and automatically measure the various base lengths of moving billets at
high temperatures, in the rolling mill in any steel plant, with higher accuracy for
minimizing measuring error and also minimizing generation of scrap. The present
new system controls the billet length by a single array(stack) of different
photosensor/phototransistors to sense the front end and a dual phototransistors,
which act as the reference/zero sensor, to sense the back end, being placed at
selective distant locations from centre of sensor stack, favoring measurement of
selective three base lengths of moving billets such as 5m, 6m and 12m with desired
degree of accuracy, decided by end uses of such billets. The signal pulses
generated by the front end and the back end sensors are logically processed to get
another pulse that represents the length of moving billet. The length is finally
indicated by said pulses on a display unit by means of selective LED indicators. The
invention also provide means for faster adjustment of the speed of flying shear
motor according to most recent measurement(from visual display unit) of a base
length by the operator directly from pulpit, such that the error of measurement is
limited to 0 to 50mm (or 0-0.3% that is further adjustable) in place of about ±
250mm obtained in conventional methods of similar measurements. Thus the
present invention has the potential for wide scale industrial applications, particularly
in measurement of base lengths of billets in rolling mill in steel plants;
BACKGROUND AND PRIOR ART:
The present invention relate to the development of the measuring system for a
continuous rolling mill of blooms to billets. Usually, 5 meter long hot blooms of
section 340mm x 300mm are rolled through ten numbers of rolling stands for
successive reduction to the section of a billet. The blooms are converted to billets of

section 105 mm xl05mm of varying continuous lengths ranging from 150 meter to
160 meter. For fulfilling the need of wire rod mill, merchant mill and other foreign
customers, the long stream of billets are cut into smaller standard base lengths e.g.
12 meter, 6 meter and 5 meter, by means of two rotating blades, also called the
flying shear which are coupled with separately excited DC drive motor with 1.1MW
capacity. The conventional method of measuring the base lengths for the rolled out
billets was achieved by the attending operator by crossing the 35 meter long cobble
prone area to measure the billet length by using the mechanical measuring scale
and running back to pulpit for adjusting the speed of flying shear motor depending
on the direction of deviation from base length noted in the last measurements.
Moreover, pneumatically operated stoppers used to stop the motion of billets to
facilitate measurement, which itself incorporated some error due to play in said
stopper in either direction. The operator was thus subjected to frequent accident in
this crude method involving physical movements/running for measurement and
adjustments in the hot cobble prone transfer zone. The conventional measuring
process thus suffered from accidents, delay and inaccuracy in measurement, high
volume of scrap and loss of productivity.
A host of factors in the said conventional process were thus responsible for and led
to variation/deviation in the standard base lengths intended to be cut from the
continuous lengths rolled out from a bloom. This in turn led to increased scrap and
loss of productivity. Such factors causing deviation of measurement of base lengths
of billets included:
Speed of flying shear motor could not be precisely adjusted as the angular velocity
of flying shear blades could not be synchronized with the linear velocity of billets in
particular ratio due to metallurgical and mechanical problems involved in rolling of
billets from hot blooms.
Parallax error in measuring cut billet length by using mechanical scale was another
factor responsible for forced deviation in measured base length, the range of
varying parallax being 30 to 50 mm.
In the conventional method the billets were measured in stationary condition, after
lifting the pneumatically operated flexible stopper which itself suffered from a play
ranging from +50mm to -50mm from its normal position.

Yet another element of error causing forced deviation of measurement of base
lengths in conventional method, was induced by delay in the measurement and also
delay in applying the correction of speed of the flying shear motor lead to generate
either longer or shorter billets, the number of such erroneous billet lengths obtained
being 8 to 14 from each bloom.
Loss of productivity was also caused in conventional method, due to the variation in
base length in a sense that the longer length billets jammed the furnaces of the
successive mills for longer times while the shorter length billets reduce the
productivity/yield of the rolling mills.
It was thus the long perceived need for developing a system of measurement of the
various base lengths of the billets in the rolling mills where they are rolled out from
blooms for continuous lengths of billet sections for required cutting by flying shear
directed to more accurate measurement of various base lengths of billets
standardized to meet the requirements of re-rolling in the wire rod mill and
merchant mill and also the demand of outside customers including the overseas
buyers. It was also the need to eliminate the limitations of the conventional
measurement method as already discussed in order to achieve quality, productivity,
safety and economy in billet rolling mill operations.
Alternative measuring systems capable to measure length of moving billets and
other similar products with precision and in a safe manner was explored in last few
years. Measuring systems involving laser and charged coupled devices were tried
during last 7-8 years in continuous casting shop with the involvement of some of
the eminent instrument manufacturers including M/s American Sensor Manufacture
Limited who tried such systems for measuring moving billet lengths but failed to
establish an accurate method to measure the even length, although the systems
were suitable for measuring dimensions of slab. The Charged Coupled Device (CCD)
Camera which was installed in blooming mill of steel plant was found to be not
suitable for application in Continuous Casting Shop(CCS) because of fluctuation in
surface temperature of slab. The system of measuring length of moving billet,
according to the present invention was thus achieved by installing a single array of
photosensors stack that takes care of wide length variation in three different base

lengths. Also a simple single array of Light Emitting Diodes (LED) displays the
respective lengths by using few digital logic gates.
The following comparative study of the present system as compared to the other
expensive alternative means for such measurement of length of moving products
like the Shaft Encoder, Laser Doppler, CCD based Camera etc. reveals its
advantages, simplicity , cost effective yet an accurate means of measurement.
A. Shaft Encoder: These instruments are capable of conducting two types of
measurements -Incremental type and Absolute type. In either type of
measurements, when applied to measure length of moving billets they are
subjected to errors/constraints due to factors like wear and tear of rolls, non-
contact/slip between rolls and billet, glitches unmeasured pulses, failure of
coupling, hydraulically pressed roll needs continuous adjustment, it needs
cooling. The error in measurement varies from 0.1% to more than 3%
depending on interval of calibration. The cost of the instrument/system is
about 0.06 million US dollars.
B. Laser based systems :(i) Laser Doppler suffers from error incorporated
due to tilting of reflecting plane of moving billet; (ii) Laser Interferometer is
subjected to system failure due to dust deposition on lens; (iii) Laser
Triangulation device needs continuous adjustments and complex circuitry has
to be maintained;(iv) Pulse radar system based on (a) time of flight and (b)
amplitude measurements, having the limitation that the object should be
visible from the laser source without obstruction, there is hardly any gap
between the two successive pieces and for accurate response the system
needs (a) 0.001 nano seconds timer, (b) roughness of reflecting plane
induces error. The Extent of error in Laser based systems ranges from
0.01% to over 0.3%. The cost including installation of a system in million US
dollars is about 0.3 for laser Doppler/interferometer, about 0.05 for laser
triangulation and about 0.01 for pulse radar device.
C. CCD Camera: This system of measurement suffer from limitations like
difficulty in sensing the edges of billets and its scaling, obstruction free area
to view for the camera that is hardly possible to be maintained at shop floor.
The system has further constraints like continuous supply of water is needed

to cool its electronic components, needs huge structure to install the system,
images obtained in the scale of 1:100/1000, at least 200mm gap is required
between two successive billets for distinctive measurement of dimensions.
The error in measurement by the CCD camera varies from 0.1% to more
than 0.3%, the threshold limit for the error percent can however be adjusted
by means of software. The cost of installation for such CCD system is around
0.02 million US dollars.
D. Load cell based system: these systems need major installation work where
in the dimensions are calculated in an indirect way by dividing
volume/weight by cross section, needing continuous calibration. The error in
measurement is also on account of variation in cross section of rolled product
by about ±10%. The magnitude of error in such systems ranges from 0.1%
to more than 0.3% and the cost of installation is of the order of 0.2 million
US dollars.
E. Orbis coil : This system can measure the total cross section but not the
height/width of the object; it is not capable to work at higher speed of
moving product; this systems suffer from poor response time; it is difficult to
install such systems in existing mills and need wide gap between edges of
two pieces to be measured distinctively.
In order to overcome the limitations of the above conventional methods, a low cost
Photo-sensor based new system of the present invention is developed on the basis
of completely blocking the view of focus object of sensors and is a distance based
system that needs no calibration on working span of time. The system is a 1:1
scaling by putting sensors 50mm away from hot moving object and need no
external cooling, no air purging for cleaning and its performance is unaffected by
any vibration of the product/roll table; such system involves simple circuit using low
cost components. The system has capability to measure dimension/length of
moving hot billets within error limit of 0% to 0.3% depending upon the least count
that is adjustable. The system is a low cost device, price of which is only about 60
US dollars.

It is thus evident from the aforesaid discussions, that the present invention is
providing a simple and low cost system of measurement of dimension/length of hot
moving billet in rolling mill of steel plants with high accuracy and reliability,
maintaining safety of the operator attending to the rolling stands for the billets. The
new system also eliminate the difficulty of measurement by the operator in the
existing system wherein he needs to run in between high temperature cobble prone
area to measure the billet lengths subsequently for its length correction thereby he
was meeting frequent accidents. The new system according to the present
invention is capable to display the base length of each billet right in the pulpit itself
and thereby ensuring safety of the operator against hot cobbled metal/billet. The
developed system also facilitate faster control on the billet length by quickly
adjusting the speed of flying shear motor according to requirement and Thus
limiting the measurement error within 0 to +50mm in place of existing level of +/-
250mm.
Also, web search on the prior art in related field of length/dimension measurement
of moving product reveaied, that such simple, safe, accurate and low cost system
involving phototransistors/photo-sensor is novel and not available in any earlier
publications/patent applications. The present invention is also capable to minimize
scrap by adopting measurement with higher precision and thereby improving
productivity/yield of the rolling mills and as such having potential for wide scale
industrial application in steel and other industries, where the system can be applied
with advantage.
OBJECTS OF THE INVENTION:
The basic object of the present invention is therefore directed to developing an
automatic system using photosensors to measure the length of moving products in
industry and in particular measuring hot moving billets in rolling mills of steel plants
in. a safe, more accurate, reliable and economical method and thereby create

substantial financial saving running into a few crores over a year by way of savings
on scrap only.
A further object of the present invention is directed to an automatic system of
measuring length of moving billets in steel plants such that the prevailing practice
of frequent unsafe hasty movement of the operator in the hot cobble prone zone in
rolling mill for measurement/adjustments is avoided to ensure operator's safety and
comfort.
A further object of the present invention is directed to an automatic system of
measuring length of moving billets in steel plants wherein each of the said photo
sensors are placed inside wooden blocks of dimension 200mmx 20mmx 16mm
which are centrally drilled for focusing and pinpointing the edges of billets from a
minimum distance of 50mm, making the device cheap yet safe even at high billet
temperatures ranging from 550°C to 1200°C. Below 550°C, method of light
interruption may be used.
A further object of the present invention directed to an automatic system of
measuring length of moving billets in steel plants, wherein a selective numbers of
photosensors are arranged in a single array for sensing the front end and a dual
photosensor as reference to sense the back end, in 1:1 configuration for distance
based measuring of said length of moving billets, on the basis of completely
blocking the view of focus object except for only viewing the ends.
A further object of the present invention directed to an automatic system of
measuring length of moving billets in steel plants, to ascertain the base lengths of
moving billets on the basis of pulses generated by the front end and the back end
sensors that are logically processed by means of an electronic processor comprising
digital IC AND/Inverter, to get another pulse that represents the length of moving
billet.

A further object of the present invention directed to an automatic system of
measuring length of moving billets in steel plants, wherein photo sensor based
measurement of moving billet is carried out with an accuracy of 0 to + 50 mm (or 0
to 0.3%) for three base length of billets for example 5m, 6m and 12m cut of
section 105mm x 105mm, from continuous lengths of 150m/160m rolled out from
blooms, to suit the intended end use.
A further object of the present invention directed to an automatic system of
measuring length of moving billets in steel plants, by said photosensor means and
the signals/pulses processed electronically to favor displaying the measured length
on a display unit in the pulpit itself and thereby facilitating faster adjustments of
speed of flying shear to control the deviations in length of billet observed to be
within the desired accuracy limit.
A further object of the present invention is directed to an automatic system of
measuring length of moving billets in steel plants, and the three base lengths
measured with higher accuracy reducing scrap and thereby improving productivity.
SUMMARY OF THE INVENTION:
The basic aspect of the present invention is directed to an automatic system of
measurement of length of moving product, such as of hot moving billets of various
base lengths in rolling mills of steel plants comprising:
photosensor/phototransistor means to measure length of moving product;
said photosensors adapted to sense the light radiation from hot billet ends, the
front and the back end of the moving billet, to favor said automatic measurement
of lengths;
said photosensors means comprising a single array of photo sensors/
phototransistors (sensor stack) in selective numbers to sense the front end and a

dual photosensor/phototransistors to sense the back end of moving product to
•facilitate said length measurement;
said automatic system of length measurement comprising, said sensor adapted to
generate electrical signals by sensing variation in the signal reception for light and
dark state that are converted to front end and back end pulses by means of a signal
processor and these pulses finally generate length pulse, combining the two end
pulses rsing logic gates, a pulse width enlarger circuit adapted to receive said
length pulse , output of which is displayed as the length of billet in the LED based
display unit.
A further aspect of the present invention directed to an automatic system of
measurement of length of moving product wherein said photosensors are
selectively disposed away from the hot product/billet to favor distance based
measurement of length of the said hot moving billet without need of calibration in
the span of time with the system adapted to conduct 1:1 scaling between
coordinate of slab and the array of photo sensors;
the number of said photo sensors "n" required for a particular base length of billet
in said automatic system of length measurement is based on:
n = {(R/Ic +1)+PS00 +PS01)} ={(R/lc+3},
where PS00 and PS0i are dual phototransistors used for sensing the back end of the
billet and are kept at a distance of (Lbx+R/2) meter from the centre of sensor stack
sensing the front end of billet, where is the minimum base length of a billet and 'R'
is the range of variability of a particular base length and lc is the least count of
measurements.
the number of said photo sensors 'n' required for measuring V number of base
lengths of moving billets in said automatic system of length measurement based
on:
n = (R/lc+1 +2x)

said automatic system of length measurement involving
photosensors/phototransistors, the length of moving billet incorporating the
theoretical measuring error , is given by:
L = {(Lbx ± a . Ic)}
Where 'a' is the serial number/position of a particular sensor in the sensor stack
with respect to the central sensor, that is activated by an approaching billet edge
within proximity of at least 50mm when the other end of the billet is leaving the
sensing range of the dual /reference/zero sensor; said serial number/location of
particular sensor sensing the characteristic dimension of a moving billet is decided
by its relative position from the centre of sensor stack; said- dual sensor is
selected/connected by means of selector switch corresponding to a particular base
length.
According to a preferred aspect of the present invention, said automatic system of
measurement of length of moving product wherein said photo sensors are
preferably placed inside soft wooden blocks adapted for independent focusing and
pinpointing of the ends of billets and to protect the sensors from high billet
temperature.
said automatic system of length measurement involving comprising, a sensor unit
generating electrical signals by sensing variation in the signal reception for light and
dark state that are converted to front end and back end pulses by means of a signal
processor, comprising simple AND and inverter digital IC and these pulses are
finally generate length pulse, combining the two end pulses, the length pulse in
turn is sent to pulse width enlarger circuit, output of which is displayed as the
length of billet in the LED based display unit.
According to an important aspect of the present invention, each of said photo
sensors are advantageously placed inside soft wooden blocks preferably of
dimension 200mmx 20mmx 16mm which are centrally drilled for independent

focusing and pinpointing of the edges of billets from a minimum distance of 50mm,
making the device cheap yet safe and accurate, avoiding expensive bakelite or
metal tube used conventionally, even at billet temperatures up to 1200°C and
without the need for cooling of the sensing unit.
According to another aspect of the present invention, in a particular embodiment of
the said automatic system of measurement of length of moving product,
particularly of hot moving billets in steel plants, to measure the base lengths of 5m,
6m and 12m, the dual photosensors were kept at a distance of 4.65m, 5.65m and
11.65m respectively to ascertain a range of 550mm in measured values of each
base lengths i.e the corresponding ranges for the three base lengths being 4.95m
to 4.4m, 5.95m to 5.4m and 11.95m to 11.4m, respectively; in a particular
embodiment of the present automatic system of length measurement the
position/location number 'a' varies from -5 to +5 in a step of 1, the total number of
sensors in the sensor stack being 11 and said zero/reference/dual sensors are three
paires in numbers selectively located to measure three base lengths of moving
billets and all its variations by involving said at least total 17 phototransistors, said
dual sensor is selected/connected by means of selector switch corresponding to a
particular base length.
In said particular embodiment of the present invention for automatic measuring of
moving billet length, the least count is 50mm for the present system ensuring the
limit of measuring error to lie between 0 to 50mm and can be adjusted based on
the accuracy desired by increasing the number of sensors for a given range, thus
minimizing further the present level of measuring error of 0 to 0.3%;
said photosensor based automatic system of length measurement of hot moving
billet in said particular embodiment, 18 phototransistors have been used for
measuring 33 different billet lengths, as process variants to three selective base
lengths e.g. 5m, 6m and 12m.

According to a further aspect of the present invention of automatic system of
measuring length of moving product, particularly of moving hot billets in steel
plants, said photosensor based measurement and subsequent signal analysis to
display the measured length, is achieved by interactive and cooperative functions of
five separate electronic circuits e.g. sensing unit, signal processing and forming end
pulses, length pulse detection circuit, output pulse width enlarger and LED length
display unit.
According to a preferred aspect of the present invention, said sensing unit of the
auotomatic measuring system having sensor stack with selective numbers of
photosensors/sensor stack for sensing the front end and said dual photosensors
sensing the back end of the moving billet of selective base lengths, comprising n-p-
n silicon phototransistors to sense light radiation from hot billet end which is
collected at the collector-base junction;
said emitter voltage from the phototransistors is sent to a signal processor wherein
it is amplified and compared with a set voltage in the respective comparator circuits
for eliminating the background light radiation and thereby favor formation of end
pulses;
said signal processor of the automatic length measuring system generate the front
end pulse by AND-ing the output of one phototransistors, with the inverted output
of the successive one in the respective quad section of logic AND gate; and the
Back end pulse is formed by processing the inverted signal of zero sensor PS0o with
non inverted signal of its pair PS0i in one of the quad section of logic AND gate,
corresponding to dual photosensor for sensing particular base length selected by
selector switch i.e. any one of three dual sensors put at 4.65m, 5.65m,11.65m
respectively from the centre of sensor stack to measure base lengths of 5m, 6m,
12m.

. said signal processor circuit of the automatic system of measuring length of moving
billets, said simultaneous occurrence of any one of front end pulse of sensor stack
is AND-ed with a back end pulse derived from dual reference/zero sensors of
particular base length such that the output of this logic AND gate produces 'Length
Pulse' which represents length of moving billet measured.
Said length pulse that represent the length of billet needing widthwise enlargement
prior to recognizable/readable display of measured length by display unit to favor
display "of output of pulse width enlarger in visually distinguishable form, as the
width of the said 'length pulse' so derived depend on the rolling speed of a
particular base length of billet and the time needed to cover the distance equal to
the least count lc in mm with a rolling speed of Sm m/sec is given by:
t = (lc /Sm) milliseconds(ms),
and that the value of't' for lc = 50mm and maximum rolling speed of Sm = 4 m/sec
comes out to be 12.5 ms which is beyond the limit of recognition response of retina
by human eye which is 20 ms.
According to a further aspect of the present invention, a simple single array of light
emitting diodes(LEDs) displays the respective billet lengths by using few digital
logic gates, activated by the said width wise enlarged length pulse, the display unit
being located in the pulpit itself for ready viewing by the operator, acting as an
interface between the measuring system and the operator.
said display unit comprise of number of LEDs needed to display a range of V base
lengths is given by:
x = d + x;
where 'd' is a particular base length.
According to yet another aspect of the present invention, in a particular
embodiment for measuring length of hot moving billets, the number of LEDs in
display unit is 14 for displaying 36 numbers of different billet lengths within the
range (550mm) of variability of measured dimensions corresponding to three base
lengths 5m, 6m and 12m by the system having specified least count of 50mm.

The present invention and its various objects and advantages are described in
further details herein below with reference to accompanying figures and non-
limiting exemplary illustrations.
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES:
Figure 1: is a schematic illustration of the layout arrangement of various elements
of a billet mill in a steel plant.
Figure 2: is the illustration of cutting operation of billets by flying shear blades.
Figure 3: is the illustration of conventional method of measuring billet length by the
operator.
Figure 4: is the schematic circuit diagram for signal processor unit illustrating
formation of front end and back end pulses.
Figure 5: is the schematic circuit diagram illustrating logic gates for generation of
length pulse.
Figure 6: is the schematic circuit diagram for length pulse display unit representing
measured length of billet.
DETAILED DESCRIPTION WITH REFERENCE TO ACCOMPANYING FIGURES:
Reference is first invited to the Figure 1 that illustrates the layout configuration of
the billet mill in a steel plant with particular illustration of the elements of the
automatic length measuring system of the present invention. The figure shows the
physical distance (shown with an double headed arrow) measuring about 35 m,
that operators (Fl: Operator is measuring length of billet; F2: Operator is crossing
/ running through cobble area; F3: Operator is in pulpit) have to move in
conventional measurement for checking length on a mechanical scale (B) and
simultaneously to control/adjust the speed of the fly sheer (A) from pulpit, as and
when necessary to rectify large deviations observed in length of billets cut on most
recent occasions. The old system also made use of pneumatically operated stoppers
(C) to stop the billets to carry out said measurement by taking the reading on
mechanical scale (B) with the billet at a stationary condition as

illustrated in figure 3. Thus the human error like parallax in taking readings on
mechanical scale amounting to 30-50mm and amount of play on the stoppers
ranging from + 50mm to -50mm and a total error in such measurement was
accumulated to about ±250mm. Moreover, the delay in measurement for time
taken to cover the distance by the operator to adjust the speed of flying sheer
according to requirement resulted in length variations, the said cutting operation
being illustrated in accompanying figure 2, longer or shorter than selected base
length, numbering about 8-14 billets per each bloom rolled into billets. The
operator also had to run the risk of moving rapidly/running in a hot cobble prone
zone and subjected to frequent accidents, apart from suffering from unnecessary
fatigue affecting his physical performance.
The automatic system of measuring the length of moving product such as moving
billets in a rolling mill (like D: Merchant Mill; E: Wire Rod Mill) in steel plants, of the
present invention involving photosensor based measurement of lengths eliminate
the perceived limitations and disadvantages of the conventional system. Figure 1
illustrates the preferred location of such photosensors/phototransistors (SS and DS)
to favor said automatic measurement directly by the operator from the pulpit itself.
This in turn facilitate the adjustments in speed of flying sheer for cutting the billets,
as necessary, from the control panel in the same pulpit.
The principle of said automatic measurement of hot moving billets is achieved in
the present invention by involving a selective number of photosensors/
phototransistors adapted to carry out a distance based measurement of billet
lengths needing no calibration in the span of time since it involves 1:1 scaling
between coordinate of billet and photosensor array, without stopping its motion and
irrespective of speed of rolling/progress. The front end of a moving billet is sensed
gradually by different phototransistors that are kept in a single array in selective
numbers depending on base lengths to be measured and the desired accuracy of
the system, called a sensor stack (SS), while the back end of the billet is sensed by
a dual phototransistor (DS) also called the zero or reference sensor located
selectively at a distance of 4.65m, 5.65m, 11.65m respectively from the center of
said sensor stack for measuring the intended base length of 5m, 6m, 12m of billets

within a range of variation of 550mm and with a least count of 50mm as illustrated
in figure 6.
The photosensors sense the light radiation from the front end and the back end of
the hot billet by means of said phototransistors, that are basically high gain two
bipolar n-p-n silicon phototransistors. They generate front end pulse(FP) and back
end pulses(BP) that are logically processed to get another pulse i.e. length
pulse(LP) that represents the length of moving billet. The width of resultant pulse
depend upon the rolling speed and it varies in the range of 6 ms to 12.5 ms and is
very difficult to be detected by operator because the retina of human eye can only
recognize the signals that are at least 20 ms wide. Therefore, the resultant length
pulse need width wise enlargement for its distinctive detection and is finally
displayed by means of glowing selective combination of LEDs in a display unit(DU)
comprising an array of LEDs in selective numbers, to represent the said enlarged
length pulse signal corresponding to a billet length, within the range and accuracy
level specified for the system.
Reference is now invited to accompanying figures 4 to 6 that illustrates the
schematic circuit diagrams for different functional units of the automatic measuring
system of the present invention. The total system is composed of five electronic
circuits/units namely (1) sensing unit, (2) signal processing and formation of end
pulses, (3) length pulse detection circuit,(4) Output pulse-width enlarger, (5) LED
display circuit/unit. The cooperative functions and interdependence of various units
to transform the light radiation sensed by the phototransistors for the two ends of a
billet length to be converted to measurement of length in a LED display unit
adaptable to display 36 different lengths corresponding to three base lengths with
their selected range of variability and least count for the system, are described
below:
The sensing Unit has the design configuration providing a linear array of
phototransistors/photodiodes that are for the first time in industrial application is
housed inside soft wooden block, instead of costly and hard bakelite block
conventionally used, with advantageous easy workability for shaping the block to
requirement and safe operation in measurement of hot moving product, such as
billets in rolling mills, from a minimum distance with desired accuracy. Such

wooden blocks are centrally drilled for focusing and pin pointing the edges of billet.
.By using wood in sensing assembly unit, the cost of overall system has been
reduced significantly.
The photosensor based automatic measuring system of the present invention is
designed to ensure a selective range of variations in different base lengths and
accuracy in measurements. Supposing the system has the range XR' meter, related
to variations in lengths of billets in different base lengths and the desired
measuring accuracy is \'(\n mm), the numbers of photosensors V required for
measuring a particular base length is given as follows:
n = {(R/Ic +1)+PS00 +PS01)} ={(R/lc+3},
where PS00 and PS0i are dual phototransistors used for sensing the back end of the
billet and are kept at a distance of (Lbx+R/2) meter from the centre of sensor stack
sensing the front end of billet, where Lbx is the minimum base length of a billet and
*R' is the range of variability of a particular base length and lc is the least count of
measurements.
The number of said photo sensors 'n' required for measuring V number of base
lengths of moving billets in said automatic system of length measurement is given
by:
n = (R/ lc +1 +2x)
In the automatic system of length measurement involving
photosensors/phototransistors, the length of moving billet incorporating the
theoretical measuring error , is given by:
L = {(Lbx ± a . Ic)}
Where 'a' is the serial number/position of a particular sensor in the sensor stack
that is activated by an approaching billet edge within proximity of at least 50mm
when the other end of the billet is leaving the sensing range of the dual
/reference/zero sensor; said serial number/location of particular sensor sensing the
characteristic dimension of a moving billet is decided by its relative position from
the centre of sensor stack.

In a particular embodiment of the present invention for demonstrating said
automatic system of measurement of length of moving product, particularly of hot
moving billets in steel plants, to measure the base lengths of 5m, 6m and 12m, the
dual photosensors were kept at a distance of 4.65m, 5.65m and 11.65m
respectively adapted to incorporate a range of 550mm in measured length data for
each base lengths i.e the corresponding ranges for the three base lengths being
4.95m to 4.4m, 5.95m to 5.4m and 11.95m to 11.4m, respectively; In this
embodiment of the present invention, only 18 phototransistors have been used for
measuring 33 different billet lengths. In said particular embodiment of the present
automatic system of length measurement the position/location number 'a' varies
from -5 to +5 in a step of 1, the total number of sensors in the stack being 11 and
said zero/reference/dual sensors are three in numbers selectively located to
measure three base lengths of moving billets, said dual sensor is
selected/connected by means of selector switch corresponding to a particular base
length.
The photosensors in the preferred embodiment for measuring different base lengths
of hot moving billets, are in particular high gain, two bipolar, n-p-n silicon
phototransistors (type 14 LF-32 Qualimatrix of USA make or equivalent of any other
make) are configured to a darlington-pair and works as an emitter follower with its
open base as shown in figure 5. The light radiation of billet is concentrated at the
collector-base junction of phototransistors and generates enough electrons. The
variation in the signal in light and dark state is sent to electronic processing unit,
kept in a control pulpit at an electrical distance of 150 meters.
The Signal processing unit receive the signal from the phototransistors and
transform the into end pulses. The emitter voltage of respective phototransistors is
amplified in quad sections of linear operational amplifiers(IC type LM-324) in
electronic processing unit. The signals are compared with set voltage of respective
comparator circuits for eliminating the background light radiation as shown in figure
5. Subsequently, the output of comparator goes to high state. In this way, the
states of all the eleven number phototransistors in the sensor stack gradually
changes. There are six numbers operational amplifiers IC LM 324 used for eleven
number amplifier circuits and the eleven number comparator circuits.

The front end pulses(FP) are formed by processing the output of a pair of
successively placed photosensors in the sensor stack(SS), wherein the out put of
the first photosensor is processed with the inverted output of second photosensors
in one of the section of quad sections logic AND gate (IC TTL type 7408). In this
way other front end pulses(FP) gradually formed by AND-ing the output of a
phototransistor with inverted output of succeeding phototransistors in other
sections of quad AND gates as shown in figure 5.
The dual photosensors(DS) PS0o and PS0i in pairs, have been put at 4.65m, 5.65m
and 11.65m respectively from the mid of sensor stack for 5m, 6m, 12m base
lengths to sense the back end of billet. The back end pulse(BP) is formed by
processing the inverted signal of PS0o with non-inverted signal of PSoi in one of the
section of quad AND gate(IC 7408). After selecting the appropriate base length out
of three different options through the selector switch provided for the purpose, as
illustrated in figure 6, the end pulse signals are sent to the length pulse detection
unit/circuit.
The length pulse detection unit is adapted to convert the front and back end pulses
corresponding to a particular billet length into a representative 'Length-pulse'CLP),
using simple logic gates. The simultaneous occurrence of any one of front end
pulse(FP) of sensor stack(SS) is AND-ed with a back end pulse derived from dual
reference/zero sensors(DS) of particular base length such that the output of this
logic AND gate produces 'Length Pulse' (LP) which represents length of moving
billet measured. The length pulse thus obtained is sent to pulse width enlarger
circuit.
The pulse width enlarger unit simply enlarges the width of length pulse formed
compatible with signals corresponding to least count of measurement into
recognizable by human eye. The output at the length pulse detection unit has a
pulse width depending on the speed of rolling and said length pulse that represent
the length of billet needing widthwise enlargement prior to recognizable/readable
display of measured length by display unit(DU) to favor display of output of pulse
width enlarger in visually distinguishable form. The width of the said 'length pulse'
is related to rolling speed of a particular base length of billet and the time needed

to cover the distance equal to the least count lc in mm with a rolling speed of Sm
m/sec is given by:
t = (lc /Sm) milliseconds(ms),
and that the value of xt' with least count lc = 50mm and maximum rolling speed of
Sm = 4 m/sec for 12m base length, comes out to be 12.5 ms, which is much less
than the limit of minimum recognition response of retina of human eye which is 20
ms. This is why a width wise enlargement of length pulse is needed and the same
is carried out by latching this signal by J-K type flip-flop IC 7474 till the arrival of
next length pulse.
The width wise enlarged length pulse signal now comes to an electronic display
unit(DU) that serves as an important interface between the operator and the
measuring system of this invention. The output pulse width enlarger is fed to LED
based billet length display unit(DU) which is installed in the operator pulpit to guide
him about the length of that billet which is recently cut. The concept of redundancy
is also applied in the use of different light emitting diodes(LEDs) as illustrated in
figure 6. A simple single array of LEDs displays the respective billet lengths by
using few digital logic gates. In the particular embodiment of the measuring system
for three selective base lengths e.g. 5m, 6m, 12m comprised 14 numbers LEDs for
displaying 36 numbers of different billet lengths, as variations for the three base
lengths within the selected range and precision of measurement. The number of
LEDs needed for display of the base lengths V is given by (d+x), where 'd' is the
number of LEDs needed to display a particular base length, as illustrate in figure 6.
The comparative study between the conventional Shaft encoder and the system of the
present invention has been conducted and the results are provided in the following table 1
and table 2.

We claim:
1. An automatic system of measurement of length of moving product, such as of hot moving
billets of various base lengths in rolling mills of steel plants comprising:
photosensor/phototransistor means to measure length of moving product wherein said
photosensors adapted to sense the light radiation from hot billet ends, the front and the
back end of the moving billet, to favor said automatic measurement of lengths;
said photosensors means comprising a single array of photosensors/ phototransistors
(sensor stack) in selective numbers to sense the front end and a dual
photosensor/phototransistors to sense the back end of moving product to facilitate said
length measurement;
said automatic system of length measurement comprising, said sensor adapted to generate
electrical signals by sensing variation in the signal reception for light and dark state that are
converted to front end and back end pulses by means of a signal processor and these pulses
finally generate length pulse by combining simultaneous occurrence of any one of the front
end pulse of the sensor stack with the back end pulse derived from the dual reference
using logic gates, a pulse width enlarger circuit adapted to receive said length pulse , output
of which is displayed as the length of billet in the LED based display unit.
2. An automatic system of measurement of length of moving product as claimed in claim 1
wherein said photosensors are selectively disposed away from the hot product/billet to
favor distance based measurement of length of the said hot moving billet without need of
calibration in the span of time with the system adapted to conduct 1:1 scaling between
coordinate of slab and the array of photo sensors;
the number of said photo sensors "n" required for a particular base length of billet in said
automatic system of length measurement is based on:
n = {(R/Ic +1)+PS00 +PS01)} ={(R/lc+3},
where PS00 and PS01 are dual phototransistors used for sensing the back end of the billet
and are kept at a distance of (Lbx+R/2) meter from the centre of sensor stack sensing the
front end of billet, where Lbx is the minimum base length of a billet and 'R' is the range of
variability of a particular base length and lc is the least count of measurements,

the number of said photo sensors 'n' required for measuring V number of base lengths of
moving billets in said automatic system of length measurement based on :n = (R/ lc +1
+2x)
said automatic system of length measurement involving photosensors/phototransistors, the
length of moving billet incorporating the theoretical measuring error, is given by:
L = {(Lbx ± a . Ic)}
Where 'a' is the serial number/position of a particular sensor in the sensor stack that is
activated by an approaching billet edge within proximity of at least 50mm when the other
end of the billet is leaving the sensing range of the dual /reference/zero sensor; said serial
number/location of particular sensor sensing the characteristic dimension of a moving billet
is decided by its relative position from the centre of sensor stack; said dual sensor is
selected/connected by means of selector switch corresponding to a particular base length.
3. An automatic system of measurement of length of moving product as claimed in anyone
of claims 1 or 2 wherein said photo sensors are preferably placed inside soft wooden blocks
adapted for independent focusing and pinpointing of the ends of billets and to protect the
sensors from high billet temperature.
4. An automatic system of measurement of length of moving product as claimed in anyone
of claims 1 to 3 comprising,
measurement of the base lengths with said dual photosensors, three pairs acting as
reference/zero sensors selectively distanced respectively from the center of sensor stack,
comprising independently focusing sensors, to ascertain a selective range in measured
values of each base lengths.
a selective least count maintained in said system of measurement, ensuring the limit of
measuring error is limited to between 0 to 50mm and can be adjusted based on the
accuracy desired by increasing the number of sensors for a given range, thus minimizing
further the level of measuring error.
5. An automatic system of measurement of length of moving product as claimed in anyone
of claims 1 to 4, comprising interactive and cooperative functions of separate electronic
circuits preferably including sensing unit, signal processing and forming end pulses, length
pulse detection circuit, output pulse width enlarger and length display unit.

6. An automatic system of measurement of length of moving product as claimed in anyone
of claims 1 to 5, wherein said photosensor based measurement comprises n-p-n silicon
phototransistors to sense light radiation from hot billet ends, being concentrated at the
collector-base junction that in turn emits enough electrons;
the emitter voltage from said phototransistors being sent to a signal processor wherein it is
amplified and compared with a set voltage in the respective comparator circuits for
eliminating the background light radiation and thereby favor formation of front end and
back end pulses;
7. An automatic system of measurement of length of moving product as claimed in anyone
of claims 1 to 6 wherein said signal processor of the automatic length measuring system
generate the 'front end pulse' by AND-ing the output of one phototransistors, with the
inverted output of the successive one in the respective quad section of logic AND gate; and
the 'back end pulse' is formed by processing the inverted signal of PS00 with non inverted
signal of PS01in one of the quad section of logic AND gate, corresponding to dual
photosensor for sensing particular base length selected by selector switch.
8. An automatic system of measurement of length of moving product as claimed in anyone
of claims 1 to 7 wherein said length pulse that represent the length of billet needing
widthwise enlargement prior to recognizable/readable display of measured length by the
display unit to favor display of output of pulse width enlarger in visually distinguishable
form, as the width of the said 'length pulse' so derived depend on the rolling speed of a
particular base length of billet and the time needed to cover the distance equal to the least
count lc in mm with a rolling speed of Sm m/sec is given by:
t = (lc/Sm) milliseconds(ms),
and that the value of 't' for lc = 50mm and maximum rolling speed of Sm = 4 m/sec comes
out to be 12.5 ms which is beyond the limit of recognition response of retina by human eye
which is 20 ms.
9. An automatic system of measurement of length of moving product as claimed in anyone
of claims 1 to 8 wherein said simple single array of light emitting diodes(LEDs) displays the
respective billet lengths by using few digital logic gates, activated by the said display
located in the pulpit itself for display of billet lengths to the operator, acting as an interface
between the measuring system and the operator.

said display unit comprising of selective number of LEDs needed to display a range
of 'x' base lengths is given by:
x = d + x;
where 'd' is a particular base length.
10. An automatic system of measurement of length of moving product as claimed
in anyone of claims 1 to 9 wherein for automatic measuring of lengths of hot
moving billets, the number of LEDs in display unit is selectively provided preferably
14 for displaying 36 numbers of different billet lengths within the range (550mm) of
variability of measured dimensions corresponding to three base lengths 5m, 6m
and 12m by the system having specified least count of 50mm.

ABSTRACT

AN AUTOMATIC SYSTEM FOR MEASUREMENT OF LENGTH OF MOVING PRODUCT
The present invention is directed to an automatic online length measuring system
for moving products including moving billets in rolling mills. The system
automatically measures the various base lengths of billets, minimizing measuring
error and reduce scrap. Moving billet length is measured by a single array of
different phototransistors to sense the front end and dual phototransistors (DS) as
reference/zero to sense the back end, placed at selective distances from centre of
sensor stack(SS), favoring measurement of three base lengths with desired
accuracy defined by selected range( R ) of 550mm and least count (lc ) of 50mm.
The front end(FP) pulse and the back end(BP) pulse from sensors are logically
processed to get the length pulse(LP) that represents the length of moving billet,
indicated on a display unit(DU) by LEDs. The speed of flying shear is adjusted by
the operator directly from pulpit and limiting the error of measurement to 0 to
50mm or 0-0.3% reducing from about ± 250mm obtained in conventional
methods.